Plug valves are commonly used to control the flow of fluids, such as hydrocarbon fluids, in pipelines and other flow containment structures. Some plug valves include slips and seals in a seat and reseat configuration. The slips are mounted to a central plug. The slips and seals operate to block fluid flow through the valve at both the inlet and outlet ports when the valve is closed. Such dual sealing action advantageously allows bleeding of the valve body while the valve is closed.
When the valve is open the slip seals are entirely removed from the fluid flow through the valve. When the valve transitions from the open position to the closed position, the plug and attached slips are first rotated 90°. Clearance between the slips and the valve body is maintained throughout the rotation to reduce actuation torque and prevent seal abrasion. When the slips are radially aligned with the inlet and outlet ports, the plug is lowered forcing the slips against the valve body and sealing the inlet and outlet ports.
When the valve transitions from the closed position to the open position the sequence is reversed. First, the plug is raised, retracting the slips from the valve body. Thereafter, the plug and slips are rotated 90° to align a flow passage through the plug with the inlet and outlet ports. Thus, both linear and rotational motion of the plug is required to open or close the valve.
A plug valve assembly may include a switching unit that monitors valve position and provides visual valve position indications and/or electrical signals indicative of the valve position to control and/or monitoring devices communicatively coupled to the switching unit.